1. Field of Invention
The invention relates to a light source driving apparatus, and, in particular, to a digital controlled light source driving apparatus.
2. Related Art
Flat panel displays have become increasingly popular in recent years, with liquid crystal displays (LCDs) garnering the most widespread acceptance. As manufacturing technology has developed, the maximum display size of the LCD is continuously upgraded for different purposes, including use as a TV display. When employed for this purpose, a flat panel LCD with a screen size of 30″ or larger is desirable. Accordingly, an LCD of this size requires a greater number of lights to provide adequate brightness.
When the number of lights is increased, however, an accompanying problem of poor brightness uniformity between lights arises. In addition, the number of light driving apparatuses for driving the lights is also increased. For example, regarding the conventional light driving apparatus, usually only two cold cathode fluorescent lamps (CCFLs) can be driven at the same time by one transformer. Thus, for an LCD with a large screen size requiring increased number of lights, the number of required light driving apparatuses is also increased, and manufacturing costs thereof increase as a result.
As previously mentioned, the conventional LCD typically employs CCFLs as backlights thereof. To induce the CCFL or CCFLs to emit light, a light driving apparatus, such as an inverter, is typically used.
Referring to FIG. 1, a conventional light driving apparatus 1 mainly includes a current adjusting circuit 11, an oscillation step-up circuit 12, a detecting circuit 13, and a feedback control circuit 14.
The current adjusting circuit 11 is controlled by the feedback control circuit 14 and properly adjusts an external DC source, which is then input to the oscillation step-up circuit 12. The oscillation step-up circuit 12 converts the input DC source into an AC signal and amplifies the AC signal. The amplified AC signal is then provided to the CCFL 2, which serves as the light, so that the CCFL 2 can then emit light. Furthermore, the detecting circuit 13 detects a feedback signal, such as a current signal or a voltage signal, from one end of the CCFL 2. The feedback signal is then transmitted to the feedback control circuit 14. The feedback control circuit 14 controls the current adjusting circuit 11 according to the feedback signal, so that the current adjusting circuit 11 can output a suitable current level. It should be noted that the conventional feedback control circuit 14 is an analog feedback control circuit.
Recently, the manufacturer has developed a method of driving a light source in a digital controlled manner. Referring to FIG. 2A, a light source driving apparatus 3 includes a digital controlled circuit 31 and a plurality of oscillation step-up circuits 32.
The digital controlled circuit 31 generates a plurality of digital switching signal sets to be respectively inputted to the oscillation step-up circuits 32 such that the oscillation step-up circuits 32 generate an alternating signal to drive a CCFL 2 to emit light.
As shown in FIG. 2B, the oscillation step-up circuit 32 typically includes two transistors 321 and 322 for receiving the digital switching signal sets generated by the digital controlled circuit 31 to control the on/off operations and thus to control a transformer 323 to generate the alternating signal to drive the cold cathode fluorescent lamp 2. However, the transistors 321 and 322 in the oscillation step-up circuit 32 have one property. The property is that the two transistors 321 and 322 cannot be turned on simultaneously, or the transistors 321 and 322 may be burned out due to the short-circuited phenomenon. The digital switching signal set generated by the digital controlled circuit 31 may cause the two transistors 321 and 322 to receive the turn-on signal simultaneously due to the crash in the digital processing step. Thus, the transistors 321 and 322 may be burned out to cause the serious result of the disabled light source driving apparatus 3.
Thus, it is an important subject of the invention to ensure the light source driving apparatus to work normally.